The present invention relates to an electric motor in which a stator core is fixed to a housing by fitting protrusions provided on the outer circumferential surface of the stator core along the circumferential direction to recesses provided in the inner circumferential surface of the housing along the circumferential direction, and to an electric compressor equipped with the electric motor.
A compressor used in a vehicle air-conditioner includes an electric compressor. A housing of the electric compressor accommodates an electric motor and a compression mechanism. The electric motor includes an annular stator and a rotor, which is located inward of the stator and is fixed to a rotary shaft. The stator includes an annular stator core and coils wound around the stator core. Fitting the stator core inside the housing fixes the stator to the housing.
In general, the stator core is fitted inside the housing by shrink fitting. That is, protrusions (for example, four), which protrude radially inward, are formed on the inner circumferential surface of the housing and are arranged at equal intervals in the circumferential direction of the housing. Then, after heating and expanding the housing, the stator core is arranged in the housing. The housing shrinks as the temperature of the housing is reduced to room temperature. The shrinkage causes the protrusions of the housing to contact the outer circumferential surface of the stator core with pressure, which completes shrink fitting.
Japanese Laid-Open Patent Publication No. 2002-281698 discloses one example of the electric motor. As shown in FIGS. 6A and 6B, an electric motor (rotating electrical machine) 100 disclosed in this publication includes a stator core 90 and a housing 92. Ribs 91 are provided on the outer circumference of the stator core 90 and are arranged at intervals in the circumferential direction of the stator core 90. Grooves 93 are formed in the housing 92 at locations corresponding to the ribs 91. Fitting the ribs 91 to the grooves 93 fixes the stator core 90 inside the housing 92.
In the above mentioned method, in which the stator core is fitted inside the housing by causing the protrusions to contact the outer circumferential surface of the stator core with pressure, regions of the stator core where the protrusions contact with pressure are pressed radially inward from a radially outer side by the protrusions. Thus, the inner circumferential shape of the stator core might deform to a shape different from the original round shape by the stress generated by the pressure. In the technique disclosed in the above publication No. 2002-281698 also, an inner bottom surface 93a of each groove 93 contacts an outer surface 91a of the corresponding rib 91 with pressure in a state where the ribs 91 are fitted to the grooves 93. Thus, regions of the stator core 90 where the ribs 91 are formed are pressed radially inward from a radially outer side by the housing 92. Therefore, the inner circumferential shape of the stator core 90 might deform to a shape different from the original round shape by the stress generated by the pressure. If such a deformation occurs, a gap between the inner circumferential surface of the stator core 90 and the outer circumferential surface of a rotor becomes uneven along the entire circumference of the rotor, which increases vibration of the housing when the electric motor is rotating.